It is well known that if the blood supply to the heart is significantly compromised and the demand of the heart for blood supply remains unchanged or increases (so called supply demand mismatch), the muscle of the heart will be irreversibly damaged in a few minutes to a few hours, depending on the severity of the mismatch and other factors. This time limit of the survival of the heart in this conditionxe2x80x94only minutes to hoursxe2x80x94presents a major challenge to physicians and exposes patients to high mortality and morbidity during myocardial infarction (heart attack). Patients may not be able to survive the heart attack or, if they do, they may develop severe heart failure due to extensive injury to the heart. This imposes a huge social and financial burden on society.
In most situations, blood supply to the heart can not be improved immediately and, if the demand of the heart for blood supply can be decreased significantly, the heart may survive this insult much longer pending further treatment and may gain enough time to recover from the insult. This is conventionally accomplished in part by keeping the patient at rest, including the use of sedatives if necessary. Also, the patient is typically given supplemental oxygen to make enhanced use of the available cardiovascular function.
The heart works as a pump to maintain blood circulation. The function of circulation is to maintain blood pressure at a certain level to provide perfusion to the organs of the body. All the prior art inventions available to artificially support circulation are designed as left ventricular supportive devices with an assumption that the heart will continue to play a central role in maintaining blood circulation. They are designed to assist the heart when it can not work normally such as a left ventricular assistant device. Alternatively, the prior art devices are intended to replace the heart""s function without considering coordination between the heart and the system, such as the cardiac-pulmonary bypass machine, which also requires a complicated procedure.
Previous inventions were designed to provide cardiac-pulmonary bypass as an assistance to the heart and allow the heart to work continuously even there is significant compromise of blood supply to the heart, or to replace the function of the heart when it fails to function. For example, U.S. Pat. No. 4,540,399 to Litzie discloses a cardiopulmonary bypass machine. It allows a physician to control the speed of the pump to maintain blood pressure at a certain level. U.S. Pat. No. 5,879,316 to Safar also discloses a cardiopulmonary bypass machine, which provides differential perfusion of different organs including the heart. It considers selective perfusion of the heart as a part of resuscitation and allows the heart to stop for one to two hours. However, it requires a complicated procedure.
A design of a pump was made public (Tokano H. et. al, World J. Surgery 9:78-88, 1985), which has EKG gating and left arterial pressure feed back to control work load on the heart. The left arterial pressure is used to determine the work load on the heart and, therefore, to control pump activity for unloading volume from the left ventricle. It is also a left ventricular assistant device and allows the heart to continue to contract and to assume a central role in circulation.
A number of inventions have disclosed cardiopulmonary bypass machines for open-heart surgery. They require insertions of a catheter into the heart chambers and the great blood vessels surgically and extensive technical support.
If a machine can maintain blood pressure, a physician can put the heart into asystole, or near asystole, without significant compromise to the function of the organs. Patients can survive without the heart""s functioning, and the heart survives until a definitive treatment takes place. The heart has enough time to recover from a transient myocardial insult.
The invention relates to a cardiac support system which can be used in conjunction with medication to render the heart in an asystolic or nearly asystolic status. It is a goal of the invention that the work load of the heart is minimized by coordination between the activities of the heart and of the system during induction and maintenance of the asystolic or nearly asystolic status and later the resumption of the normal activity of the heart.
Because the invention allows a physician to put an acutely diseased heart into an asystolic or nearly asystolic status, the physician has enough time to perform further diagnostic tests and therapeutic intervention, and to transfer the patient to a referral center for further treatment. The invention is designed with the concept that the heart needs to stop working if its blood supply is significantly compromised. It is also a consideration of the invention that the pump system disclosed herein is easy to use by most medical practitioners in most medical facilities throughout the world.
No previous invention has been designed with the concept of intentionally rendering the heart temporarily asystolic or nearly so in order to allow adequate time for the performance of diagnostic tests, therapeutic maneuvers, and recovery from the myocardial insult. To achieve this goal, the device and the heart need precisely coordinated activity. This may be achieved by a complex interaction between the electromechanical activity of the heart and the device. None of the prior art devices teaches adequate mechanisms for coordination between the heart and pump activity. It is important to have mechanisms of coordination between the cardiopulmonary pump and the heart when attempting purposeful induction and maintenance of an asystolic or nearly asystolic status.
For example, ""399 does not take it into account that the heart needs to stop working. Neither ""399 nor ""316 teach intentional cessation of the heart as a primary treatment instead of as a resuscitation attempt or as a part of open heart surgery. Neither patent has a mechanism to sufficiently coordinate the contraction of the heart with the activity of the cardiopulmonary bypass machine, such as EKG gated pump activity with interaction between pressure control and EKG gating, although some of them did have EKG gated activity and pressure feedback. Although there are EKG gating and pressure control (only left atrial pressure feed back) devices known in the art, there is no interaction among EKG, arterial pressure, contraction of the heart and pump activity.
The invention provides a method of facilitating cardiac rest in a human comprising induction of a controlled asystolic state in the human and application of life support techniques while the human is in the asystolic state.
Typically, the induction includes administration of a medication or medications such as calcium channel blockers, beta adrengenic blockers, antiarrhythmics and potassium. These drugs are well known in the art. Examples of calcium channel blockers include verapamil and diltiazem. Examples of beta adrenergic blockers (or beta adrenergic receptor antagonists) include propranolol, esmolol and bretylium. Examples of antiarrhythmic agents include lidocaine, adenosine, procainamide and quinidine.
Some of the medications can be placed in more than one category. For instance, the beta blockers can be useful as antiarrhythmic agents. If potassium is used to slow or to stop the heart, intravenous potassium chloride is a preferred embodiment. For this purpose, the potassium is administered in a large vein or a central vein, such as the femoral, jugular or subclavian vein. Other drugs may be administered as is well known in the art. For example, pain killers and sedatives may be indicated. Examples include morphine, phenobarbital and diazepam.
Life support techniques of the invention include application of a closed extra-corporeal circulation system. Such a system typically includes a venous conduit, a gas exchanger, a pump for pumping at least a portion of the patient""s blood, and an arterial conduit. Preferably, the artificial circulation system is arranged such that the venous conduit is connected to a vein of the patient, the arterial conduit is connected to an artery of the patient, the gas exchanger is connected to at least one of the venous conduit and the arterial conduit, and the pump is connected to at least one of the venous conduit and the arterial conduit. Usually the gas exchanger is adapted both to remove at least a portion of a quantity of carbon dioxide from the patient""s blood and to add a quantity of oxygen to the patient""s blood. A heat exchanger may be included, and it is connected with any two of the group comprising the arterial conduit, the pump, the gas exchanger, and the venous conduit. Preferably, the pump included in the circulation system is a pulsatile pump.
The closed system preferably includes an EKG gating mechanism that has an EKG sensor means for sensing the human""s heartbeat, and a feedback means for coordinating the EKG sensor means with the pump wherein the pump discontinues for a time of at least one heartbeat sensed by the EKG sensor means and resumes pumping when the heartbeat is not sensed by the EKG sensor means at a rate or at a volume which is needed to maintain blood pressure above a preset level and is controlled by an intrinsic rate or volume setting.
The closed system may include an arterial pressure sensor that has a feedback means for coordinating the arterial pressure of the human with the pumping of the pump such that the pump changes at least one of pumping rate and pumping volume when the pressure sensor senses a pressure different from a predetermined arterial pressure range. The pressure sensor is also used to re-initiate the pump activity after EKG gating means stops the pumping activity as described herein and when the blood pressure sensor senses a fall in blood pressure.
The pump increases a volume output of the pump by changing at least one of pump rate and pump volume when the pressure sensor senses an arterial pressure less than the predetermined arterial pressure and decreases a pumping rate when the pressure sensor senses an arterial pressure higher than the predetermined arterial pressure.
The closed system includes a gating coordination means for coordinating the EKG sensor means with the arterial pressure sensor means. To promote adequate arterial blood pressure in the human, the pressure sensor means is adapted to override the EKG gating means to control the pump for at least one of pumping rate and pumping volume.
The pump preferably includes at least two chambers. The two chambered pump is coordinated such that one of the chambers is receiving blood into itself while the other of the chambers is emptying blood from itself. The closed system further includes a QRS reset mechanism that is adapted to sense a QRS complex generated by the patient and to reset the pump""s pumping when the QRS complex is sensed by the reset mechanism. In this embodiment, the resetting of the pumping is accomplished such that the chamber that was receiving blood before the reset will resume receiving blood until a predetermined volume is received, and such that the chamber emptying blood will resume emptying blood until a predetermined volume is emptied.
The invention further provides a method of facilitating cardiac rest in a patient comprising induction of a state of either reversible bradycardia or reversible asystole in conjunction with the application of life support techniques. Bradycardia can refer to a heart rate of from 1 to 60 beats per minute. Alternatively, bradycardia can refer to a heart rate of from 1 to 10 beats per minute.
Additionally, the invention provides a method of facilitating cardiac rest in a patient who has sustained a cardiac insult comprising induction of a controlled state of lowered metabolism of the myocardium of the human. This state includes decreased heart rate and decreased oxygen utilization. During this time, life support techniques are administrated including extra-corporeal circulation through a closed system. The closed system has a pump, a gas exchanger, a heat exchanger, and a systolic gating mechanism. The controlled state of lowered metabolism facilitates further treatment to the heart without injury to the heart or compromise of blood supply the other vital organs.
The gas exchanger is typically adapted to remove C02 from and to add 02 to at least a portion of a volume of blood pumped through the closed system. Also, the gas exchanger is usually located in series between a vein of the human and the pump.
Preferably, the systolic gating mechanism is adapted to coordinate the pump and systole such that the pump is restrained from pumping during systole. The gating mechanism preferably includes a pressure sensor and a feedback means to the pump. The feedback means is adapted to control at least one of pumping rate and cardiac volume output. Typically, at least one of the pumping rate and the volume output is sufficient to maintain a predetermined pressure.